Decabromodiphenyl oxide (deca) and decabromodiphenylethane (deca-DPE) are commercially available materials widely used to flame retard various polymer resin systems. The structure of these materials is as follows:

One of the advantages of using deca and deca-DPE in polymer resins that are difficult to flame retard, such as high-impact polystyrene (HIPS) and polyolefins, is that the materials have a very high (82-83%) bromine content. This allows a lower load level in the overall formulation, which in turn serves to minimize any negative effects of the flame retardant on the mechanical properties of the polymer.
Despite the commercial success of deca, there remains significant interest in developing alternative halogenated flame retardant materials that are equally or more efficient, not only because of economic pressures but also because they may allow lower flame retardant loadings, which in turn may impart improved performance properties. Improved properties, such as non-blooming formulations, or better mechanical properties can potentially be met by producing polymeric or oligomeric flame retardant compounds. These types of materials tend become entangled in the base resin polymer matrix, depending on the compatibility between the resin and the flame retardant, and hence should show fewer tendencies to bloom.
There are a number of commercially available flame retardant materials that can be considered oligomers or polymers of halogenated monomers. Examples of these monomers include tetrabromobisphenol A (TBBPA) and dibromostyrene (DBS), which have the following structures:

Commercially, TBBPA and DBS are typically not used in their monomeric form, but are converted into an oligomeric or polymeric species. One class of oligomers is the brominated carbonate oligomers based on TBBPA. These are commercially available from Chemtura Corporation (examples include Great Lakes BC-52™, Great Lakes BC-52HP™, and Great Lakes BC-58™) and by Teijin Chemical (FireGuard 7500 and FireGuard 8500). These products are used primarily as flame retardants for polycarbonate and polyesters.
Brominated epoxy oligomers, based on condensation of TBBPA and epichlorohydrin, are commercially available and sold by Dainippon Ink and Chemicals under the Epiclon® series, and also by ICL Industrial Products (examples are F-2016 and F-2100) and other suppliers. The brominated epoxy oligomers find use as flame retardants for various thermoplastics both alone and in blends with other flame retardants.
Another class of brominated polymeric flame retardants based on TBBPA is exemplified by Teijin FG-3000, a copolymer of TBBPA and 1,2-dibromoethane. This aralkyl ether finds use in ABS and other styrenic polymers. Alternative end-groups, such as aryl or methoxy, on this polymer are also known as exemplified by materials described in U.S. Pat. No. 4,258,175 and U.S. Pat. No. 5,530,044. The non-reactive end-groups are claimed to improve the thermal stability of the flame retardant.
TBBPA is also converted into many other different types of epoxy resin copolymer oligomers by chain-extension reactions with other difunctional epoxy resin compounds, for example, by reaction with the diglycidylether of bisphenol A. Typical examples of these types of epoxy resin products are D.E.R.™ 539 by the Dow Chemical Company, or Epon™ 828 by Hexion Corporation. These products are used mainly in the manufacture of printed circuit boards.
DBS is made for captive use by Chemtura Corporation and is sold as several different polymeric species (Great Lakes PDBS-80™, Great Lakes PBS-64HW™, and Firemaster CP44-HF™) to make poly(bromostyrene) type flame retardants. These materials represent homopolymers or copolymers. Additionally, similar brominated polystyrene type flame retardants are commercially available from Albemarle Chemical Corporation (Saytex® HP-3010, Saytex® HP-7010, and PyroChek 68PB). All these polymeric products are used to flame retard thermoplastics such as polyamides and polyesters.
Unfortunately, one of the key drawbacks of the existing halogenated polymer materials is their relatively low halogen content, which makes them less efficient as flame retardants and consequently typically has a negative effect on the desirable physical properties of the flame retardant formulations containing them, such as impact strength. For example, whereas deca and deca-DPE contain 82-83% bromine, oligomers or polymers based on the brominated monomers mentioned above generally have a bromine content in the range of 52%-68%, depending on the material. This therefore typically requires a flame retardant loading level in a polymer formulation significantly higher than that required for deca, often resulting in inferior mechanical properties for the formulation.
In our U.S. Patent Application Publication No. 2008/0269416, we have proposed a new class of flame retardant materials that to not detract from the mechanical properties of the target resin and that are based on halogenated aryl ether oligomers comprising the following repeating monomeric units:
wherein R is hydrogen or alkyl, especially C1 to C4 alkyl, Hal is halogen, normally bromine, m is at least 1, n is 0 to 3 and x is at least 2, such as 3 to 100,000. These materials can be halogenated to a higher level than other currently available oligomeric flame retardants and provide superior mechanical properties when combined with resins such as HIPS and polyolefins as well as engineering thermoplastics such as polyamides and polyesters. It is also found that these aryl ether oligomers, even at lower levels of halogenation, give formulations with acceptable mechanical properties.
The materials disclosed in the '416 publication are polymeric in the sense that they have a molecular weight distribution resulting from the varying degrees of polymerization of the monomer units. According to the invention, we have now found that certain discrete halogenated phenyl ether compounds, which have multiple phenyloxy linkages but which are not polymeric in the sense that they do not have a molecular weight distribution, have utility as flame retardants. Moreover, when blended with analogues having different numbers of phenyloxy linkages and formulated into polymer resins, such as high-impact polystyrene, these materials provide flame retarded resin compositions having similarly improved physical properties, as obtained with their polymeric counterparts.
Japanese Unexamined Patent Application Publication 2-129,137 discloses flame retardant polymer compositions in which the polymer is compounded with a halogenated bis(4-phenoxyphenyl)ether shown by general formula [I]:
in which X is a halogen atom, a and d are numbers in the range of 1-5, and b and c are numbers in the range of 1-4. Various levels of bromination are discussed in this application, but there is no disclosure of blending the halogenated ether with materials having different numbers of phenoxy groups. Also it will be seen that all the phenoxy groups in the compound of formula [I] are linked to the adjacent phenyl group in the 4- or para-position.
U.S. Pat. No. 3,760,003 discloses halogenated polyphenyl ethers having the general formula:
wherein each X is independently Cl or Br, each m is independently an integer of 0 to 5, each p is independently an integer of 0 to 4, n is an integer of 2 to 4, and 50% or more by weight of the compound is halogen. The ether linkages on the non-terminal phenyl groups can be in the meta or para position and the materials are said to be flame retardants for a wide variety of polymer resins. Again, however, there is no reference to blending ethers with different n values.
In an article entitled “Synthesis and Stationary Phase Properties of Bromo Phenyl Ethers”, Journal of Chromatography, 267 (1983), pages 293-301, Dhanesar et al disclose a process for the site-specific bromination of phenyl ethers containing from 2 to 7 benzene rings. The ethers appear to be discrete compounds with no oligomeric distribution and, although the products are said to be useful in the separation of organic compounds, no reference is given to their possible use as flame retardants.